Say you're a dude, and you've always loved muscles and jumping, and then you hit 40 and your muscles just aren't as jumpy as they used to be and your jumps aren't as muscly and also your penis seems to have stopped listening to you and begun forging its own path, and you just kind of want to take a nap at what used to be high-jump-boner-o'clock. Let's say you're that guy. Would you spend $400 for a glug from a supposed fountain of youth? What if your doctor said it was okay? But what if the FDA didn't?

Testosterone therapy—administered at "Low T Centers" around the country—is the panacea du jour for men who are feeling a little less than fresh. But the procedure is only FDA-approved for "medical conditions associated with a deficiency or absence of endogenous testosterone (primary or secondary hypogonadism)," not the gradual decrease in testosterone that's a natural part of aging.

David Von Drehle at TIMEwonders: Is that safe? And is it even effective?

Testosterone "is believed to accelerate the growth rate of known prostate cancers," is associated with "serious and possible life-threatening heart and blood-vessel problems, such as heart attack, stroke, blood clots and increased or irregular heart rate," and, it seems, might at least partially be a placebo.

Aging men by the millions are finding themselves soft where they would prefer to be firm and dull when they really need to be sharp. And although the Food and Drug Administration (FDA) doesn't exactly approve of it, a growing number of men have come to believe that hormone therapy is the answer. Sisk is happy to oblige. With 49 clinics in 11 states–and more to come–his chain of Low T Centers serves 45,000 patients, he says, at an average price per patient of about $400 per month.

...But given the unknowns of testosterone therapy, should aging men by the millions be juicing themselves with substances powerful enough to keep Barry Bonds and Roger Clemens out of the Hall of Fame? Not to mention the risk to people close to them: men who apply the gel should be careful not to let it come into contact with others. In pregnant women, T-gel exposure can cause birth defects, and in all women it can cause abnormal hair growth and acne. In kids, it can cause enlarged genitals and, in boys, increased erections.

...Sisk puts it this way: "Our dads' generation went quietly into the night." Smiling broadly, he continues, "My generation is not going quietly."